Early refrigeration units used ammonia and sulfur dioxide to lower temperature through evaporation. These substances were quite dangerous, however, and a search for a stable and odorless liquid was pursued. American chemist Thomas Midgleyhad discovered such a liquid in 1921, but it was not until 1930 that he synthesized a substance with these properties. Trademark uses were established, and such products as Freon, deemed completely safe at the time, went on sale and were used in refrigeration units. A 1931 survey by twenty leading refrigerator manufacturers revealed that three million Americans protected their food through the use of electric refrigerators. In 1930 1,002,000 refrigerators were sold. Of these, 770,000 were household refrigerators sold for a total of $223,320,000, or approximately 31 percent of the value of all household electric appliances. Nevertheless, these impressive numbers paled when compared to the number of American homes actually equipped with refrigerators: 14.7 percent, mostly...